This invention was conceived to extend the life of tooling used to punch holes in metals especially thick steel members. During the punching process shear energy is developed by the tooling to produce the cut. Friction between the tool (said tool is referred to as a punch) and the metal being punched (said metal is referred to as the work) develops a force normal to the shear forces which develops heat and is detrimental to the tool. This friction force can be reduced by providing a lubricant in the immediate vicinity of the shear area. For maximum effectiveness the lubricant must posses a high amount of lubricity and must be of proper viscosity to be transported to the cutting area and then the viscosity must be much lower to allow flow between the tool and the work.
Most punching processes mount the punch vertical and the work is held below the punch. Lubricant is applied to the punch prior to punching. A problem with lubricants presently used is the viscosity is so low the lubricant runs off the tool prior to the punching process rendering the lubricant ineffective. My invention solves this problem by modifying the viscosity of said lubricant to make it thixotropic. Thixotropy is a property a fluid posses when its viscosity changes with the introduction of shear energy into the fluid. The ratio of the viscosity at low internal shear energy to the viscosity at high internal shear energy is referred to as thixotropic index. The thixotropic index of my invention is controlled to provide the proper viscosity to keep the lubricant on said punch and then during the punching process the viscosity is reduced sufficiently by the shear energy applied between said punch and said work to allow the lubricant to flow in the shear area thereby providing maximum lubrication between the punch and the work.